Mullite and corundum prepn - with raw materials preheated in shaft kiln

摘要

Method of making mullite, corundum, or zircon containing minerals, from a raw mix containing clay, aluminium silicate, alumina, gamma-alumina, magnesium oxide zirconium silicate alone or in admixture and aluminium fluoride by feeding the raw mix, opt. after a preforming and preheating stage, into a shaft prior to the firing zone in a kiln whose upper part is at a temp. of at most 400 degrees C, in practice 100-200 degrees C, sucking off the flue gases from the upper levels of raw mix and finally burning the material in a stationary of rotating firing zone under or neare the shaft at a temperature of at least 900 (1350) degrees C. Accelerated rate of mullite formation, reduced loss of F in the flue gases. The raw materials is reacted at at most 800 degrees C with a mixture of alkali(ne-earth) fluoride or silico-fluoride and H2SO4. Altenatively, it can be treated with a fluorine bearing gas at least 1,700 degrees C.